1. Field of the Invention
The present invention relates to an imaging apparatus comprising an optical magnification changing mechanism and an electronic magnification change mechanism.
2. Description of the Related Art
In a video camera or a digital camera having a zoom lens system, a zoom ratio is changed by moving a zoom lens, whereby a focal distance is changed to a telephoto side or a wide-angle side while a focal position is kept constant, thereby changing an object distance. However, when configuring a small imaging element, optical zooming from the wide-angle side to the telephoto side changes not continuously but in a stepwise manner when a design is made such that a group number of lenses is decreased.
As shown in FIG. 10, an optical system includes: a first lens group 1001 having a negative refractive power, the first lens group being fixed during magnification change or focusing; and a second lens group 1002 which moves during magnification change or focusing, sequentially from an object side. In the optical system, an image surface changes in a curved shape as illustrated in the case where a position of the second lens group 1002 has been moved as illustrated. Because there is only one group of drive sections, a focus and an image magnification unavoidably change at the same time, and a configuration desired by a user cannot be always produced.
In the case where the object has moved to a position which corresponds to a curve indicated by a′ while focusing is carried out for an object which corresponds to a curve indicated by “a” shown in FIG. 10, an angle of view moves to the wide-angle side by carrying out focusing.
As is obvious from FIG. 10, a′ is close to an infinite point compared with “a”. That is, when an object of interest is distant near a wide angle, an angle of view moves to the wide-angle side due to focusing, resulting in unnatural feeling. In addition, in the case of the telephoto side, the object is made distant, whereby the angle of view becomes small. In this case, the object is made distant, whereby an expansion direction is obtained, and thus, a problem is not so serious as that at the wide-angle side.
On the other hand, as shown in FIG. 12, when lens types 1031, 1032, and 1033 having positive, negative, and positive configurations, respectively, are used, the object is made distant at the wide-angle side, whereby the object is zoomed in. In some cases, a preferable result is obtained. However, at the telephoto side, the angle of view changes in a wider direction due to focusing with respect to a distant object. In this case, a framing change occurs due to lens focusing rather than framing intended by the user, and this change is unavoidably used. Further, there occurs a problem with focusing and framing of a still object as well.
FIG. 13 is a view adopted to explain this problem. In FIG. 13, as a result of that the user focuses with an attempt to image objects “a” and “b” while intending to obtain an angle of view 1022, the angle of view 1022 appears like an element 1023, and part of the object “b” becomes missing.
Furthermore, in the case of macro imaging, a focal change is large, and thus, a change of an angle of view is also large. However, a zoom optical system in which only one group shown in FIGS. 10 to 12 is movable can reduce the number of lenses and can simplify a drive section. This makes possible a configuration of stepwise zooming while achieving downsizing and low cost.
Jpn. Pat. Appln. KOKAI Publication No. 6-339083 discloses that magnifications of a two-focus optical system and an optical finder with a zoom are coincided with each other by using a magnification changing process with electronic zooming. A technique of compensating for a change of an angle of view at the time of focusing by means of electronic zooming is disclosed in Jpn. Pat. Appln. KOKAI Publication Nos. 2002-182302 and 11-23949, in which unnatural feeling of the user is reduced by smoothly changing a magnification of electronic zooming to a target magnification. In addition, Jpn. Pat. Appln. KOKAI Publication No. 2003-283910 discloses that, in order to substantially match angles of view of an optical finder and imaging system while a drive control system of the optical finder and a stepwise zooming imaging lens is used in common, the stepwise zooming at a magnification, which does not exceed a magnification of the optical finder but is proximal thereto, is selected when the magnification is specified, and adjustment of an angle of view is carried out by electronic zooming.
On the other hand, in recent years, a video camera has incorporated an electronic zooming function for electronically changing an image magnification by using an imaging element other than such optical zooming. The electronic zooming function is a function of changing a focal distance to the telephoto side without moving a zoom lens so as to convert an imaging signal in the region which is smaller than a light receiving screen area of the imaging element to a video signal which corresponds to the light receiving screen size.
In a video camera having such an electronic zooming function, an imaging region which is greater than the area of the image sensor cannot be obtained. For this reason, zooming to the wide-angle side has not be successfully achieved although zooming to the telephoto side can be achieved. In contrast, there is proposed an apparatus and a method for substantially generating an image at the wide-angle side while fixing a lens by utilizing a difference between the number of pixels of the imaging element and the number of pixels of an output image. An imaging apparatus enabling such electronic zooming includes an imaging apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2000-295530, for example. This publication discloses a solid state imaging apparatus having photoelectric conversion pixels arranged two-dimensionally, for randomly providing an access to the photoelectric conversion pixels, the apparatus comprising first skipping means for reading out an arbitrarily specified pixel in an arbitrarily specified region and second skipping means for reading out an image region which is smaller than an image frame read out by the first skipping means, wherein the number of pixels read out by the first and second skipping means are made equal to each other.
Further, Jpn. Pat. Appln. KOKAI Publication No. 10-42183 discloses an imaging apparatus comprising: first adjusting means for optically changing an angle of view of an image; a second adjusting means for electrically changing an angle of view of an image; and control means for controlling the first adjusting means and the second adjusting means to determine an angle of view, wherein the control means has been configured to adjust an angle of view to a desired angle of view by the second adjusting means and substantially move the control of the angle of view from the second adjusting means to the first adjusting means while maintaining the angle of view. The imaging apparatus uses a CCD type imaging element. When electronic zooming is carried out, all pixels are read out from the CCD type imaging element, and the read-out pixels are temporarily stored in a frame memory or the like. Then, an electrical interpolating process is carried out on the basis of a pixel signal relating to a small number of pixels included in a partial area of a full angle of view.
Moreover, Jpn. Pat. Appln. KOKAI Publication No. 2002-314868 discloses an imaging apparatus using an imaging element which is capable of specifying a readout position and range on the imaging element by reading out a photoelectric conversion signal on the imaging element in accordance with an X-Y address system, and further, carrying out thinning-out readout based on the same number of clocks. There is disclosed that the imaging apparatus makes control by using electronic zooming means for carrying out electronic zooming for changing an isolation angle of view which is obtained as an isolation range of an imaging position and an imaging angle of view; and the electronic zooming and optical zooming in combination, whereby a zooming range of an output angle of view associated with a finally output image signal is controlled so as to be substantially wider than any of an optical zoom range which can be produced by only a change of the imaging angle of view and an electronic zoom range which can be produced by only a change of the isolation angle of view.
In addition, Jpn. Pat. Appln. KOKAI Publication No. 2002-249968 proposes a method of reducing distortion of an image obtained during readout with respect to distortion of an image caused by thinning-out readout by using spatial and temporal interpolation, and obtaining a high quality image, wherein a step width of the thinning-out readout can be finely produced to a certain degree.